Fluid-operable device including a piston for controlling flow through a pair of ports



United States Patent FLUID-OPERABLE DEVICE INCLUDING A PISTON FOR CONTROLLING FLOW THROUGH A PAIR OF PORTS 7 Claims, 2 Drawing Figs.

U.S. Cl." 137/625.66 Int. Cl ..FI6k 11/06,

Fl6k 31/363 Field ofSearch 137/625.66

References Cited UNITED STATES PATENTS 3,107.692 10/1963 Forwald l37/625.66 3,392,742 7/1968 Diver l37/625.66X

Primary Examiner-Henry T. Klinksiek Auurne \'-Mawhinney and Mawhinney ABSTRACT: A valve of the kind including a piston movable in a housing to control flow through a pair of ports in the hous ing. the piston having two alternative operative positions in each of which the piston is held from movement by outofbalance forces due to the pressure of said fluid acting on faces of the piston of unequal effective area, the piston also having a pair of oppositely-directed faces additional to its faces subjected to said fluid and each bounding one of a pair of chambers in the housing, each chamber receiving a trigger pressure signal to be applied temporarily to the appropriate one of said chambers to reverse the direction of the resultant force acting on said piston to cause said piston to move towards its other operative position in which it will be held by out-of-balance forces acting thereon due to the pressure of said fluid after said trigger pressure signal has been removed.

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INVENTORz- COLIN JOHN KIRK ATTORNEY FLUID-OPERABLE DEVICE INCLUDING A PISTON FOR CONTROLLING FLOW THROUGH A PAIR OF PORTS The invention relates to a fluid-operable device of the kind including a piston movable in a housing therefor to control flow through a pair of ports in the housing and is particularly concerned with a piston forming a valve member but may also be applied to a piston arranged to transmit shaft or fluid power.

According to the invention, a fluid-operable device of the aforesaid kind includes a piston having two alternative operative positions in each of which the piston is held from movement by out-of-balance forces due to the pressure of said fluid acting on faces of the piston of unequal effective area, the piston also having a pair of oppositely-directed faces additional to the faces thereof subjected to said fluid and each bounding one .of a pair of chambers in the housing, each chamber being arranged to receive a trigger pressure signal to be applied temporarily to the appropriate one of the chambers to reverse the direction of the resultant force acting on thepiston, thereby to cause the piston to move towards its other operative position in which it will be held by the out-ofbalance forces acting thereon due to the pressure of said fluid after the trigger pressure signal has been removed.

Conveniently, one of the ports is an inlet for said fluid and is arranged to communicate under the control of one end face of the piston with said other port, which is arranged to communicate with an outlet for said fluid under the control of an oppositely-directed face of the piston, said one port being open and said other port being closed when the piston is in one of its operative positions and said other port being open and said one port being closed when the piston is in the other of its operative positions, the effective areas on the faces of the piston subjected to said fluid being such that when said one port is open and said other port is closed, the resultant of the out-of-balance forces acting on the piston acts to hold the piston in said one operative position and when said one port is closed and said other port is open, the resultant of the out-ofbalance forces acting on the piston acts to hold the piston in said other operative position, until the application to the piston of the appropriate trigger pressure signal.

By using out-of-balance forces to maintain the piston in either of its operative positions and by using a trigger pressure signal to reverse the resultant of the out-of-balance forces, the piston is driven over from one operative position to the other by the rate of flow and the pressure of said fluid and not by the value of the trigger pressure signal, and thus the speed of actuation of the piston is determined by the pressure and flow capacity of the ports being controlled instead of by the valu of the trigger pressure signals.

Each end face of the piston may be arranged to overlap the respective port when closing it, whereby the effective area of the end face of the piston subjected to the pressure of said fluid when the respective port is closed is less than the effective area when the respective port is open. Such an arrangement has the disadvantage that leakage of fluid to exhaust can occur during the change-over from one operative position of the piston to the other. To overcome this disadvantage, the piston may alternatively have at each end thereof a cylindrical extension of smaller diameter than an adjacent intermediate portion of the piston and sealingly insertable within the respective port, the axial lengths of the extensions being such that said one port will be closed before said other port is opened and vice versa, the effective area of each end face of the piston when the respective port is closed being the crosssectional area of the extension only and the effective area of the end face of the piston when the respective port is open being the full cross-sectional area of said adjacent intermediate portion of the pistons.

By way of example, a valve in accordance with each of the two immediately preceding paragraphs will now be described with reference to the accompanying drawings, in which:

FIGS. 1 and 2 are respectively axial sections through the two valves.

Referring to FIG. 1, the first valve comprises a housing 1 containing a piston 2 movable between two operative positions in which the piston closes the adjacent end of one or other of a pair of pipes 3 and 4, forming the aforesaid ports. in the position illustrated, the pipe 3 is closed by the right-hand end face of the piston 2 and the pipe 4 is open. The piston is movable to the left into its other operative position in which the pipe 4 will be closed by the left-hand end face of the pistoh and the pipe 3 will be open. The two end faces of the piston'2 are of greater diameter than the bores of the pipes 3 and 4 and are provided with valve seats 5 and 6 respectively for effecting seals against the ends of the pipes 3 and 4. The pipe 3 is an inlet for fluid being controlled and the pipe 4 communicates externally of the valve with an annular space 7 within the housing 1 surrounding the pipe 3, either directly or througha piston to be operated by movement of the valve. The external communication between the space 7 and the pipe 4 is indicated by the pipe 20, the space 7 and the pipe 4 could conimunicate with opposite ends of a power-producing piston (not shown). When the piston 2 has been moved to the left from its illustrated position, fluid will flow from the inlet pipe 3, through the space 7 and the communicating pipe 20 to the pipe 4, or it may move a piston in place of the pipe 20 and that piston will displace fluid to the pipe 4. When the piston 2 has been moved to the right into the illustrated position, the inlet pipe 3 will be closed and the pipe 4 will open to an annular exhaust indicated by 8. Intermediate the two ends of the piston 2 there is a shoulder 9 between a larger diameter portion 10 of the piston and the left-hand end thereof. The shoulder 9 forms one wall of an annular gallery 11 surrounding the piston 2 and communicating via a duct 12 with the right-hand end face of the piston 2. At all times the inlet fluid pressure available at the pipe 3 communicates via the duct 12 with the annular gallery 11 and so acts against the shoulder 9 in opposition to the force due to the inlet pressure acting on the right-hand end face of the piston 2.

The piston 2 has a circular flange 14 of larger diameter intermediate the shoulder 9 and the right-hand end face arranged to run in another annular gallery 15 formed in the housing. The annular gallery 11, and the two portions of the gallery 15 at the leftand right-hand ends of the flange 14 are sealed by means of O-rings 16 mounted on the piston 2. The leftand right-hand end portions of the annular gallery 15 are provided with inlet ports 17 and 18 respectively to which trigger pressure signals can be applied.

in FIG. 1, the bore area of each pipe 3 and 4 is equal and is indicated by A; the area of the left-hand end of the piston 2 is indicated by C greater than area A, and the area of the righthand end of the piston 2 is indicated by C also greater than area A. The area of the shoulder 9 is B and this is greater than the area A by an amount A The trigger pressure signals applied to the leftand right-hand end portions of the gallery 15 are indicated by S and S respectively. The area C is equal to area A plus area B plus an area A and may either be equal to or less than the area C When the piston 2 is in the right-hand operative position as illustrated, the inlet pressure S in the pipe 3 acts against the.

right-hand end face of the piston 2 over area A and also acts in the opposite direction against the shoulder 9 over area B. The piston 2 will remain in this position as area B is greater than the area A by an amount A, and there will be an out-ofbalance force acting to the right equal to S (BA) =S X A The piston will remain in this position until a trigger impulse pressure S is temporarily-applied through the pipe 18 to apply a force greater than S X A,. As soon as the piston 2 has moved towards the left, pipe 3 opens, the fluid force acting to the left will be S X C and the force acting to the right will be S X B. As the area C is greater than area B, the piston 2 will move to the left-hand operative position in which it will close the pipe 4. This movement is independent of the value of the trigger pressure signal S and is determined by the rate of flow and pressure of the-fluid admitted through the inlet pipe A. When the piston 2 has moved fully into the left-hand operative position,

it will remain in that position until a trigger pressure signal S is applied through pipe 17, since there is an out-of-balance force on the piston 2 acting to the left equal to S X C: S X B S X A. The latter term is due to the pressure applied through the communication 7 and the pipe 4 against the left-hand end face of the piston 2. The resultant out-of-balance force is therefore S X A When the trigger pressure signal S, is applied through the pipe 17, the out-of-balance force acting on the piston will be reversed and the piston 2 will move to the right. As soon as the pipe 4 has been opened, the pressure applied therethrough will fall to the exhaust pressure and the piston will move fully to the right.

FIG. 2 shows an alternative valve device which differs from the device shown in FIG. 1 in that the piston 22 which is slidable in a housing 21 is provided with smaller diameter cylindrical end extensions 25, 26 which are sealingly slidable within the pipes 23 and 24 respectively. The axial lengths of the extensions 25 and 26 are such that when the piston 22 is moving to the right, the left-hand extension 26 will not leave the pipe 24 before the extension 25 has entered the pipe 23 and similarly when the piston 22 is moving to the left, the extension 25 will not leave the pipe 23 until the extension 26 has entered the pipe 24. Therefore except in the extreme leftand right-hand operative positions, the pipes 23 and 24 will both be sealed by the piston 22. This prevents leakage of fluid and therefore results in more efflcient operation of the valve. As in FIG. 1, the piston 22 has a shoulder 29, similar to shoulder 9, slidable in an annular gallery 31. There is an internal duct 32, similar to the duct 12, for admitting fluid from the inlet pipe 23 to the annular gallery 31. There is a central flange 34, similar to the flange l4, dividing an annular gallery 35 into two portions to which trigger pressure signals S and S; can be applied through ports 37 and 38 respectively. The two portions of the gallery 35 and the gallery 31 are sealed by means of rings 36 carried on the piston 22. The ends of the extensions 25 and 26 carry O-rings 37 making sealing engagement with the pipes 23 and 24. There is an annular exhaust 28, similar to the exhaust 8 in FIG. 1, and as in FIG. 1, there is an external communication indicated by a pipe 40 between the annular space 27 around the inlet pipe 23 and the pipe 24. The pipe 40 may be replaced by power-producing pistons, not shown, to the opposite ends of which the space 27 and the pipe 24 communicate. Areas of the piston 22 and the pipes 23 and 24 are indicated by A, B, C and C similarly to like areas in FIG. 1. The out-of-balance forces which will hold the piston 22 in either of its operative positions until the application of a trigger pressure signal S or are the same as those set outin connection with the valve shown in FIG. 1.

Although the two valves illustrated in FIGS. 1 and 2 are valves of the poppet kind, the pistons 2 and 22 could be piston valves controlling ports provided in a cylindrical wall of the respective housing. Instead of the piston 2 or 22 controlling an external power-transmitting piston connected in the place of the pipe or 40, the piston 2 or 22 could itself be used for transmitting power either by fluid pressure or by means of a piston rod.

I claim:

1. A fluid operable device of the kind including a piston movable in a housing therefore to control flow through a pair of ports in the housing, the piston having two alternative operative positions in each of which the piston is held from movement by out-of-balance forces due to the pressure of said fluid acting on faces of the piston of unequal effective area, wherein the improvement comprises a pair of oppositelydirected faces on said piston additional to said faces thereof subjected to said fluid and each bounding one of a pair of chambers in the housing, each said chamber including a port for receiving a trigger pressure signal to be applied temporarily to the appropriate one of the chambers to reverse the direction of the resultant force acting on said piston to cause said piston to move towards its other operative position in which it will be held by out-of-balance forces acting thereon due to the pressure of said fluid after said trigger pressure signal has been removed. h I

2. A device as claimed in claim 1 in which one of the ports is an inlet for said fluid and communicates with an outlet for said fluid under the control of an oppositely-directed face of said piston, said one port being open and said other port being closed when said piston is in one of its operative positions, and said other port being open and said one port being closed when said piston is in the other of its operative positions, the effective areas of the faces of said piston subjected to said fluid being such that when said one port is open and said other port is closed, the resultant of the out-of-balance forces acting on the piston acts to hold said piston in said one operative position and when said one port is closed and said other port is open, the resultant of the out-of-balance forces acting on said piston acts to hold said piston in said other operative position, until the application to said piston of the appropriate trigger pressure signal.

3. A device as claimed in claim 2 in which each end face of said piston overlaps the respective port when closing it, the effective area of the end face of said piston subjected to the: pressure of said fluid when the respective port is closed being less than the effective area when the respective port is open.

4. A device as claimed in claim 2 in which said piston has at each end thereof a cylindrical extension of smaller diameter than an adjacent intermediate portion of the piston and sealingly insertable within the respective port, the axial lengths of said extensions being such that said one port will be closed before said other port is opened and vice versa, the effective area of each end face of the piston when the respective port is closed being the cross-sectional area of the extension only and the effective area of the end face of the piston when the respective port is open being the full cross-sectional area of said adjacent intermediate portion of the pistons.

5. A device as claimed in claim 2 in which said piston has a shoulder thereon having an end face directed oppositely to said one end face of said piston and defining an annular gallery in said housing, said piston having a passageway therein leading from that part of said one end face which is always in communication with said one port to said annular gallery.

6. A device as claimed in claim 2 in which said piston has an intermediate portion of larger diameter than end portions of said piston and said housing includes an annular gallery at each end of said intermediate portion, said chambers to which the trigger pressure signals are applied being formed by said annular galleries.

7. A device as claimed in claim 1 in which said piston is employed to transmit power externally of the housing. 

